In an incident that may have been caused by improper weight and balance onboard, an Air Canada 737 MAX 8 rotated on its own, forcing pilots to hold the nose down until the aircraft obtained sufficient takeoff speed.
Air Canada 737 MAX 8 Rotates On Its Own During Vancouver Takeoff
The incident, noted in the Aviation Herald, occurred on December 19, 2021 utilizing a Boeing 737 MAX 8 (C-GEKX) and performing AC234 from Vancouver (YVR) to Edmonton (YEG). 166 passengers and eight crewmembers were onboard.
Rotation is the action of applying back pressure to a yoke or other control device in order to lift the nose wheel off the ground during takeoff.
When the nose rose expectedly, pilots were able to push it down and keep it down until the aircraft gained enough speed for takeoff. The incident is likely attributed to a weight imbalance in the cargo hold, though that is not clear.
Last week I wrote about the Emirates 777-300ER takeoff incident from Dubai and was pleased at how many pilots chimed in. I hope the same is true here, particularly some who may fly the 737 MAX. My questions:
- What could have caused this incident?
- Had the pilots failed to keep the nose down, would the plane have been able to lift itself off the ground?
- Does this happen on other plane types?
CONCLUSION
An Air Canada 737 MAX 8 rotated on it owns, at least ostensibly pointing to an aft-heavy cargo hold. I’m particularly curious about this incident because I was not aware that an aircraft rotate on its own while speeding down a runway.
image: Air Canada
I saw this as well and was intrigued. In reading the comments in AV Herald (many are commercial pilots) the cause seems suspect. The one thing they all agree on though is questioning why the hell did the pilots continued the flight?
Further, a few have chimed in that in no way would 89 bags have that kind of affect on a 737Max. One thing we know for sure, there are going to be a lot of people looking at this.
There is cargo as well as the “89” pieces of luggage/baggage etc. on board. Also the passenger arrangement might have added to this cause. This might also be due to an entirely different reason.
Yes, other than a weight problem, a mis set stab trim can also cause the nose to rise on its own. Northwest Airlines had such an incident in 2000, when the weight data indicated a -1 stab setting and the crew set +1. The aircraft rotated well before V1 and resulted in altitude of about 50’ when the crew rejected the takeoff and resulted in a hard landing.
I hope the pilot landed and the cargo was reloaded to fall within the aircrafts established c of g limits. If this was an improper loading issue, it had nothing to do with the aircraft being a Boeing Max 8 737 and the aircraft didn’t “rotate on its own” it was simply human error . This one is on Air Canada.
That was my first reaction. This is not a trivial problem and cause further problems on landing.
…and how are you such an expert on this particular incident?!
I agree with what Chris said. Stabilizer trim is an adjustment that sets a tab on the horizontal tail of the aircraft called the elevator. Air flow over that tab deflects the elevator up or down to reduce the amount of force required to the flight controls in order to climb or descend. On landing approach the trim might be around 8 or 9 units of up elevator or basically climb trim in order to fly with full landing flaps (30 or 40 degrees) at around 135 knots normally. The takeoff trim setting is much lower as we only use a small fraction of the available flaps (1 or five degrees) for takeoff, and we accelerate to more than 200 knots, requiring less up elevator pressure or “back stick” pressure on the yoke.
If the pilots are distracted by a runway change or a maintenance item they can unintentionally omit a checklist which would normally catch their mistake. This could result in improper flap settings, trim settings, and other potential hazards. I think this hypothesis would be the most likely cause of an unintended rotation on takeoff.
As far as whether to abort the take off in that scenario, it’s dangerous to abort a takeoff above 80 knots unless there’s a fire, engine failure or severe damage which would make the aircraft unable to fly. The correct procedure would be to continue the takeoff unless they thought the aircraft would not fly. The faster you are, the more dangerous it is to abort. Many aircraft have crashed attempting to abort at high speeds when they would have been safer getting airborne and handling the emergency and checklists once safely away from the ground, thus the procedure to continue takeoff above 80 knots unless certain criteria are met.
Even if the issue was weight and balance, why would the pilots when take off? Because airborne it could easily have gone nose up and the rest could have easily been history
I was on a WestJet flight from JFK to YYC a couple of years ago, window seat just behind the wing, starboard side, watched the loading, then watched the unloading to another door, 30 minutes late TO, the pilots obviously new the balance, why didnt the AC pilots note it and have it rebalanced, AC flight control centre gave the OK I presume but still the captains preogitive to over ride it.
Depending on the length of the runway, the weight of the aircraft and other factors they aircraft probably had already exceeded its V1 speed. Once a aircraft passes V1 in most circumstances pilots are trained to takeoff and deal with the issue in the air, An aircraft isn’t a car and it can’t stop on a dime and if your on a short runway you don’t have enough concrete ahead of you to safely stop the aircraft on the ground before running out of usable runway. The pilots made the right call by holding the nose down until they reached they reached Vr V2.
That leaves the question, why did they not return to the YVR instead of continuing the flight?
A tail heavy situation isn’t cause for an emergency landing and the 737 can’t jettison fuel so they would have had to burn off some fuel anyway before attempting to land. Also the flight could have been tail heavy do to the load master giving the flight crew incorrect information. If the pilots were given incorrect information that means the aircraft takeoff configuration was wrong. This is something can be fix in the air while enroute by adjusting the aircraft trim settings on the horizontal stabilizers. Adjusting the trim settings would counter the tail heavy out of balance situation there is no need to return to the departure airport.
And the new MCAS software “fix” did not resolve this issue???
You don’t understand what MCAS is or how it operates.
Agreed. Why would you continue accelerating after that, unless you didn’t have enough runway to abort. Personal, I find a CG out of aft limits to be one of the scariest things in flying. I always triple check it. I’ve seen too many crashes where there pilots has zero options after takeoff and were just along for the ride.
It’s more likely that bad load numbers were input into the weight and balance system. The stab trim must be set within a pre-determined range for takeoff or a warning horn will sound when the throttles are advanced for takeoff. The 737 has the ability to generate its own C.G. through a balance sensor in the nose wheel well, and therefore a stab trim setting. Any large difference between that and what the load people send would be investigated by the crew.
Are these sensors only on the max? Can you elaborate on how they work?
“When the nose run expectedly, pilots were able to push it down and keep it down ”
How do you do that?
The yoke right in front of the Pilot controls that action.
D.A. …. MCAS would have absolutely nothing to do with this incident. When activated, which can only occur in airmode, it would push the nose down not up.
I agree with other comments questioning why the crew continued with the takeoff and also potential stab out of trim condition.
You comment is totally out of context and not worth considering
I would hope that when prior to landing in YEG that an offload audit was requested and compared to the close out at the origin. Not sure if AC usees scanners planeside to designate whats loaded in each cargo area. It would be quickly determined by YEG if the offload matched those figures. Its not just bags, but also mail, freight. Often the loads are split not only between forward and aft compartments, but forward or aft within those compartments. Scanners will normally alert the user if there is significant departure from the plan. Failure to properly set the compartment locations on the scanner prior to loading can cause a misload. Weight and balance discrepancies are FAA reportable and trigger investigation with the loading ramp crew.
This is an aerodynamics issue specifically associated with 737 max design. Putting larger diameter engines forward moves lefting point forward as well. When the lifting point goes over the center of gravity, automatic rotation, an unstable aerodynamic phenomenen, happens. The worst scenario is a variable lefting point depending on attack angles. The original MCAS is designed to counter this effect.
I have read similar as to the design which, interestingly, affected airlines seat placements in the rear. However, if still the case, at what point do we ask if an aircraft is safe that has such a low threshold margin of error? Most pilots commenting in AvHerald are of the same thought, that 89 bags in the rear instead of forward should not have any affect in the performance of a large commercial aircraft.
rough figures 89 bags X 30 lbs = 2670 lbs
I work ramp for an airline that flies the max 8 and we typically load them tail heavy. This is because of the heavier engines up front as opposed to the 737-800, we typically load those nose heavy. When we flew the 737-300 we loaded those tail heavy and if you looked at the 700 and 300 side by side there was more fuselage ahead of the engines on the 300 vs the 700.
As others have noted you have two likely causes for this event.
1. The aircrafts center of gravity was off from what had been calculated. This could have resulted in a stabilizer trim setting that allowed or caused the aircraft to rotate early as a result of the CG condition.
2. The stabilizer trim was set incorrectly resulting in enough nose up force to create an uncommanded rotation.
Again as noted by others this would have happened at a relatively high speed and the fact that the pilots were able to control the airplane by pushing the nose back down means that an abort was not required and undesirable. The pilots from what we know right now did the right thing by pushing the nose down until rotation speed and then flying away.
Its very possible the gate check bags were at a all time high. Greedy passengers try take all the worldy possesions and dont want to pay the check fee. The average weight is calculated per bag but i believe the bags were very very heavy. Also it could of been a weight discrepency with the actial cargo that was loaded. This week of flights had cargo at a all time high.
Yes, it must be the fault of those “greedy passengers,” how dare they not want to pay their fair share to the benevolent and unselfish airline, lol. It’s not like the airline weighs them at check-in and has people load them on the plane. The airline had no idea of how much weight was in the cargo areas.
When Boeing managers decided they were also engineers.
A friend who works for Air Canada cargo says they are understaffed and overworked. Says cargo.is not being properly balanced and someday it will cause problems. Maybe this was the day.
To answer two of those questions; Yes, it definitely happens in other types.
One of which I’m familiar was caused by the flight attendants accidentally transposing the passenger count numbers for the forward and aft sections of the aircraft’s cabin. The THS setting was incorrect causing the Airbus A320 to rotate early.
This results have concluded there excesive passenger bags loaded in the aft and were data inputed for the front.. dont you hate greedy passengers that over pack and dont pay
https://www.flightglobal.com/safety/details-emerge-of-second-air-canada-737-max-load-imbalance-incident/147038.article